Adding DI to existing RO system

[KenAdams]

Hi guys, new reefer here. I bought a used BRS dual stage DI to add to my existing RO system. I want to still have normal RO at the sink and am ok with having my DI out location (where I fill my buckets) also near/under the sink. I thought the connection would be a very simple T from the product water line that goes to the faucet to divert the reef water needed through the DI canisters & keep the faucet water nomal RO.

I've connected everything & water flows through the DI canisters just fine but the output shows no improvement on TDS. The cartridges were purchased used so my first thought was that they were simply depleted but on the resin appears brand new & undepleted. The seller included a partial bag of unused resin & I did confirm the resin is the color changing type when I asked. I did not think to ask how long the resin in the cartridges had been used for, but on visual inspection they appear to be fresh and the same dark color as the unused resin in the bag. Also, the bag with the unused resin has a shipping sticker on it showing July of 2024 and I assume the resin in the cartridges came from the same bag since it only has a little left in it so the resin doesn't seem to be old/outdated. I've ordered new resin regardless knowing I'll need some later but I don't think the resin is the problem.

Another thought I had was that I should probably have a check valve in the line to prevent backflow from the RO to the DI canisters but that certainly wouldn't cause enough backflow to render the DI canisters completely ineffective, which is where I'm currently at since the water coming out of the DI cannisters has no TDS improvement. I could see a slight degradation from backflow but not to this extent. I've ordered one that will arrive tomorrow anyway.

I'm including a diagram picture in the hopes someone can maybe spot where my error is. Thanks so much.

 

[Crabs McJones]

Welcome to R2R!

What is your TDS out of the RO membrane? If the RO is getting weak and the TDS is too high the DI may not be able to do an efficient job.

 

[KenAdams]

It's at 20 coming out of the RO faucet & 28 after going through the DI canisters so somehow it's gaining TDS by going through them. I've ordered new filters and I'll see if that changes anything but I didn't order a new membrane as it's less than a year old and also because it wouldn't be a factor in the resin not reducing the TDS after going through the membrane.

 

[KenAdams]

Update: I ordered new resin from BRS & when I opened it the first thing I noticed was that it was blue & clear beads vs the very purple looking stuff given to me by the seller. I switched out his resin for the new stuff & it worked (nearly) perfectly. I'm still getting 1-3 TDS but I can work with that. I'm hoping that will get corrected when I swap out new filters on the RO canisters.

I read some other threads on here talking about a type of resin that is purple, so that might be what he had given me. I have no idea if they are color changing, but he said they were & they seem to be solid color throughout so they wouldn't appear to be depleted, but for whatever reason they weren't working to reduce TDS.

The beads are solid purple throughout & don't show signs of color variation/change, so if anyone knows what it is or could give some insight on what it's useful for that would be great because I hate to throw it out. I just know I can't use it as it is in the existing cartridges because it was ineffective.

 

[Shirak]

Purple is usually Cation resin. If they are colored they are color changing. Not many cations get through the RO membrane so the cation resin depletes very slowly.

What did you put in the canisters now? is it mixed bed?

 

[KenAdams]

What did you put in the canisters now? is it mixed bed?

Yes, the 1.25 lb mixed bed from Bulk Reef Supply. Not the Pro, just the one that says Bulk Deionization Resin. It doesn't say mixed bed in the product title but it mentions it in the description.

 

[Shirak]

Yes, the 1.25 lb mixed bed from Bulk Reef Supply. Not the Pro, just the one that says Bulk Deionization Resin. It doesn't say mixed bed in the product title but it mentions it in the description.

What is the tds of your source water and RO water? You should be getting 0 out of the DI. Did you confirm the in and out on both DI canisters to make sure water is flowing in the correct direction and the inserts are inserted right side up?

 

[Shirak]

What do you mean RO at the faucet? Is there an RO spigot with a pressurized RO tank? I think I would put an on off valve between the RO T and the DI canisters so you can shut them off when not filling buckets.

 

[KenAdams]

What is the tds of your source water and RO water?

500-600 on the source water, 15-20 out of the RO. I am now getting 0 TDS readings on the RODI after cleaning the probes on my meter & also cleaning the bucket a 2nd time. I am using a bucket that has been used for other things before (never held chemicals) and cleaned it once but I went through with a second deep clean.

 

[KenAdams]

What do you mean RO at the faucet? Is there an RO spigot with a pressurized RO tank?

Yes.

I think I would put an on off valve between the RO T and the DI canisters

I have one, although I installed it after the DI canisters instead of where you suggested. You can see it in the pic in my original photo where the DI tubing is resting in a temporary clear bucket.